Method And System For Manufacture Of A Wire Cage

ABSTRACT

A wire cage making machine includes a pair of rod supporting wheels decoupled from one another and capable of being rotated by respective motors at different speeds and/or directions to control the contour of a wire cage, such as twisting the rods. The machine includes a carriage to which the wheels are mounted, with one of the wheels maintained at a fixed position on the carriage and the other wheel movable along rails of the carriage. A welding head is positioned proximate the stationary wheel and is connected to the carriage by a pivot arm that allows the welding head to be moved closer to or farther away from the center of the stationary wheel. The pivot arm allows the position of the welding head to be moved in response to changes in radial positions of longitudinal rods carried by the wheels and to which wire is welded, to join the rods together to form a wire cage. The rods are held by clamps mounted to spokes of the wheels. The radial position of the clamps of the stationary wheel can be moved in real-time to change the diameter of the wire cage.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. Ser. No. 60/913,166,filed Apr. 20, 2007, the disclosure of which is incorporated herein byreference.

BACKGROUND AND SUMMARY OF THE INVENTION

Wire cages are commonly used as the reinforcing structure for concretepipes and other cast concrete products. Typically, the wire cagesconsist of a series of longitudinal steel rods interconnected by acircumferential spiral wire that is welded to the longitudinal rods.Wire cages are made using a machine composed of a pair of wheels; one ofwhich is stationary and the other of which is movable. The wheels carryclamps that hold the rods as the spiral wire is welded to the rods. Thewheels are mechanically coupled to one another by a drive shaft that isrotated by an electric motor to synchronize rotation of the wheels toincrementally present the steel rods and spiral wire to a welding unit.More particularly, the electric motor spins the drive shaft, which thenthrough gears and a chain mounted on the outer edge of both wheels,causes the wheels to rotate. These mechanical connections candeteriorate over time, thereby causing inconsistencies in the rotationalvelocity of the wheels and ultimately defects in the finished wire cage.

Thus, in one aspect, the present invention is directed to a wire cageforming machine in which the two wheels are not mechanically coupled toone another by a drive shaft. Each wheel is rotated by a separate drivemotor, and feedback from the drive motors is used to control therotational speed of the wheels. For instance, the motors may becontrolled by a programmable logic controller (PLC) and arranged in amaster-slave arrangement. The rotational speed of the movable wheel maythus be controlled to match the rotational speed of the stationarywheel.

With a conventional wire cage making machine, the wheels are rotated atsubstantially same speed by the drive shaft. As such, the longitudinalrods are uniformly aligned along the length of the wire cage. That is,the rods are not only parallel with one another along the length of thewire cage, but the angular position of the rods relative to the centeraxis of the wire cage is constant along the entire length of the rods.This can be problematic for wire cages used in the concrete pipeindustry, as the concrete pipe manufacturing machinery can twist thewire cage while the concrete is being formed around the wire cage. Thistwisting may cause torsional stress in the wire cage, and once theconcrete pipe is released from its mold the wire cage has a tendency tostraighten from the twisted state back to its original configuration.This can cause cracks to form in the concrete pipe. Thus, it may bedesirable to intentionally twist the rods of the wire cage during thecage making process, so as to counteract the rotational forces appliedto the wire cage by the pipe-making equipment during production of theconcrete pipe.

Twisting the rods using a conventional cage making machine is generallynot possible given the mechanical coupling of the wheels. The presentinvention, however discloses decoupled wheels that are separately drivenby respective electric motors. The electric motors can thus becontrolled to rotate the wheels at different speeds or in oppositedirections to twist the rods during production of the wire cage.

In accordance with another aspect, the invention discloses a frictionwheel drive for rotating the wheels. The friction wheel drive reducesvibrations in the cage making machine and therefore provides forsmoother operation at higher rotational speeds. In addition, it isbelieved that the friction drive is more reliable and less prone topremature mechanical failure.

The wheels of a conventional wire cage making machine include centralhubs and spokes extending from the hubs to outer annular rims. Eachspoke carriers a rod clamp capable of holding a longitudinal rod at twodifferent radial positions. Thus, the wire cage making machine can makea wire cage having one of two diameters. A single wire cage havingcertain lengths at one diameter and other lengths at a differentdiameter may be made by manually changing the position in the clampwhere the rods are held, but this is a labor intensive process and, assuch, can be costly.

In accordance with another aspect, the present invention discloses anapparatus capable of adjusting the radial spacing of the longitudinalrods without requiring manual repositioning of the rods in theirspoke-mounted clamps. Moreover, the apparatus allows the radial spacingto be changed in real-time. In general, the apparatus includes a chainmount slidable along a guide tube. An actuator pushes or pulls the chainmount toward or away from the hub of the stationary wheel. As the chainmount is translated along the guide tube, the radial position of the rodclamps, which are connected to the chain mount by chains, is varied. Theradial position of the clamps can be changed independent of the rotationof the stationary wheel. Accordingly, the apparatus of the presentinvention may be used to produce a wire cage having any desireddiameter. In addition, the diameter of the wire cage can be varied asthe cage is being produced, the provide a cage having any desiredprofile.

Various other features, objects and advantages of the invention will bemade apparent from the following description taken together with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the best mode presently contemplated of carryingout the invention.

In the drawings:

FIG. 1 is an isometric view of a wire cage making machine having astationary wheel and a movable wheel which are separately andindependently driven by respective drive motors, which allows the wheelsto be rotated at different speeds and/or different directions, accordingto one aspect of the invention;

FIG. 2 is a top plan view of the wire cage making machine of FIG. 1;

FIG. 3 is a front end elevation view of the stationary wheelincorporated in the wire cage making machine of FIG. 1;

FIG. 4 is a front end view of the movable wheel incorporated in the wirecage making machine of FIG. 1;

FIG. 5 is a front isometric view of the stationary wheel end of the wirecage making machine of FIG. 1, showing a welding head mounted to a pivotarm proximate the stationary wheel, according to one aspect of theinvention;

FIG. 6 is a schematic of a welding unit incorporated in the wire cagemaking machine of FIG. 1, according to one aspect of the invention;

FIG. 7A is a simplified section view of a cage diameter control systemincorporated in the wire cage making machine of FIG. 1, coupled to thestationary wheel and having a chain mount positioned at a first linearposition along a guide tube to position rod clamps mounted to spokes ofthe stationary wheel at a first radial position;

FIG. 7B is a simplified section view of the cage diameter control systemsimilar to FIG. 7B, with the chain mount at a second linear positionalong the guide tub to position the rod clamps at a second radialposition along the spokes of the stationary wheel;

FIG. 8 is a schematic diagram of a wire cage produced using the wirecage making machine of FIG. 1, with uniformly aligned longitudinal rods;

FIG. 9 is a schematic diagram of a another wire cage produced using thewire cage making machine of FIG. 1, with twisted longitudinal rods; and

FIG. 10 is a schematic diagram of a wire cage produced using the wirecage making machine of FIG. 1, with twisted longitudinal rods andvariations in cage diameter along the length of the wire cage.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a system and method for making wire cages thatmay be particularly useful for reinforcing concrete pipe or othertubular concrete structures. A wire cage generally consists of a seriesof longitudinal rods interconnected by a circumferential or spiral rodor wire that is welded to the longitudinal rods at each point at whichthe circumferential rod or wire intersects the longitudinal rods. A wirecage making machine 10 is shown in FIG. 1 and is composed of fourgeneral components or systems: a rod support frame or carriage 12, acage diameter control system 14, a welding unit 16, and a controlstation 18. Each of these systems will be described in greater detailbelow, but generally these systems provide increased flexibility indefining the contour of a wire cage. It is noted that a wire cage makingmachine may have additional components or systems not specificallydescribed herein.

Rod Support Carriage

Referring to FIGS. 1, 2 and 4, the rod support carriage 12 includes astationary wheel 20 and a movable wheel 22 supported by a frame 24. Theframe 24 includes a pair of rails 26, 28 that support the movable wheel22 and house a pair of racks 30, 32, respectively, along which themovable wheel 22 may be translated to pull longitudinal rods through thestationary wheel 20, as will be explained further below. The framefurther includes a base 34 that supports the stationary wheel 20. Themovable wheel 22 is translated along the racks 30, 32 by a drive motor36 that drives a pair of pinions 38, 40 through a drive shaft 41, alongthe pair of racks 30, 32. In operation, longitudinal rods are fedthrough the stationary wheel 20 and fastened to the movable wheel 22.During the cage making process, the movable wheel 22 is moved away fromthe stationary wheel 20 by operation of the drive motor 36 rotating thepinions 38, 40 to move along the racks 30, 32, until a desired cagelength is reached. It should be noted that the carriage 12 may supportmore than the one movable wheel shown in the figures.

The movable wheel 22 is comprised of an annular rim 42, a hub 44, and aseries of radially spaced spokes 46 connected between the rim 42 and thehub 44. A cover 48 generally encloses a bottom half of the annular rim42 to prevent unintended contact with the movable wheel 22. Each spoke46 carries a rod clamp 50, each of which holds the end of a respectivelongitudinal rod during the cage making process. The rod clamps 50 alsohold their respective rods as the wheel is rotated about a central axis52 extending through the hub 44.

The movable wheel 22 is supported on a carriage 53, to which drive motor36 is mounted. The movable wheel 22 is supported for rotation oncarriage 53 by a central axle oriented along axis 52, which is rotatablymounted within a suitable bearing 55 that is secured to carriage 53.

The movable wheel 22 may be rotated in either a clockwise orcounterclockwise direction by a drive motor 54, which drives a roller56. The drive roller 56 frictionally engages and drives the annular rim42 in a controlled manner, so as to impart rotation to wheel 22 inresponse to operation of drive motor 54. It is understood that any othersatisfactory type of driving engagement between drive motor 54 and rim42 may be employed, such as a gear or chain drive.

With additional reference to FIG. 3, the stationary wheel 20 is similarin construction to the movable wheel 22. The stationary wheel 20includes an annular rim 58, a center hub 60 aligned with axis 52, and aseries of spokes 62 that extend between, and are connected to, the hub60 and the rim 58. Each spoke 62 also carries a rod clamp 64 thatretains a respective longitudinal rod but does so in a manner thatallows the rods to be pulled through the wheel 20 as the movable wheel22 is moved.

The stationary wheel 20 is also rotatable about the central axis 52 by adrive motor 65, which rotates a drive roller 66. An annular ring 59 ismounted to the annular rim 58, and the drive roller is engaged with ring59 to frictionally drive or rotate the annular rim 58. Alternatively, itis understood that any other satisfactory type of driving engagementbetween drive motor 65 and ring 59 or rim 58 may be employed, such as agear or chain drive. The stationary wheel 20 is partially encased by agenerally arch-shaped bulkhead 68. Rollers 70, 72, and 74 are mounted toan inside surface of the bulkhead 68 and ride along ring 59. Rollers 70,72, and 74 function to stabilize and guide movement of the wheel 20 asit is rotated.

In one representative embodiment, the stationary wheel 20 and themovable wheel 22 are each frictionally driven by their respective drivemotors and rollers. This is in contrast to gear and chain drive systemsthat are typically employed to rotationally drive the wheels.Frictionally driving the wheels 20, 22 reduces vibrations therebyproviding smoother operation at higher rotational speeds. The drivemotors are controlled by a programmable logic controller (PLC), withdrive motor 54 used as a slave motor and drive motor 65 used as a mastermotor. In this configuration, the stationary wheel 20 will act as themaster and the rotational velocity of wheel 20 will be calculated by thePLC. The velocity of the movable wheel 22 is then calculated and througha feedback system the rotational velocity of movable wheel 22 iscorrelated to the rotational velocity of the stationary wheel 20. In anapplication in which a cage having straight longitudinal rods, therotational velocity of movable wheel 22 is made to match that ofstationary wheel 20. This feedback system also allows the slave motor 54to rotate the wheel 22 at an advanced or retarded pace relative to thestationary wheel 20, to provide the longitudinal rods with a spiral orzig-zag configuration, when desired. This provides considerable benefitsand flexibility in the manufacture of wire cages for variousapplications.

In the illustrated embodiment, a drive shaft does not extend between thewheels (in contrast to known prior art). However, it is understood thatthe wheels could be connected to a common drive shaft that is rotated bya single drive motor, e.g., drive motor 65 when it is desired that thewheels be rotated in unison. For such an embodiment, a clutch or similardevice could be used to disconnect the wheels from the drive shaft whenit is desired to separately rotate the wheels.

Welding Unit

As shown in FIGS. 1, 3, and 5, the welding unit 16 is positionedproximate the stationary wheel 20 and generally includes a power unit 76and a welding head 78. The welding head 78 is mounted to an arm 80 thatis pivotably attached to the frame or carriage 12, such as rail 28. Moreparticularly, the arm 80 is pivotably supported by a pivot pin that isengaged with a bracket 82 attached to the rail 28. The bracket 82 allowsthe arm 80 to pivot about the pivot pin to accommodate for variations inthe diameter of the cage, as will be explained further below.

The power unit 76 is supported by a stanchion 84 to which a pair ofcylinders 86, 88 are mounted. The cylinders 86, 88 include rams 90, 92,respectively, that are coupled to the arm 80. When the rams 90, 92 areextended, the arm 80, and thus the welding head 78, is pivoted aboutbracket 82 to move welding head 78 inwardly. Likewise, when the rams 90,92 are retracted, the arm 80, and thus the welding head 78, is pivotedabout bracket 82 to move welding head 78 outwardly. In one embodiment,the cylinders are hydraulic cylinders, but other types of cylinders oractuators may be used, such as pneumatic cylinders, or similarmechanized devices, such as screw drives or other linear actuators.

The welding head 78 is designed to spot weld wire circumferentiallyaround the longitudinal rods extending between the wheels 20, 22 thatform the body of the wire cage. The welded circumferential wireeffectively joins the longitudinal rods together to form the cage. Inthis regard, the circumferential wire is fed from a wire supply 94, FIG.1, to the welding head 78. The circumferential wire is guided by anarcuate guide channel 96 supported by table 98, which may be integrallyformed with the frame or carriage 12. The circumferential wire is fedthrough a eye 99, and is held against the guide wall by rollers 100 thatare supported by the table 98. The wire is then threaded through rollers102 and a pinch 104. From the pinch 104, the wire is passed underrollers 106, 108 that are mounted to arm 80, and is then fed to thewelding head 78 for welding to the longitudinal rods.

During the cage making process, the circumferential wire is presented tothe welding head 78, which spot welds the circumferential wire to thelongitudinal rods extending through the stationary wheel 20 and held bythe movable wheel 22 as the longitudinal rods are rotated by the wheels20, 22 and moved axially away from the stationary wheel 22 by movementof movable wheel 20. The spot welding operation is carried out as thestationary and movable wheels 20, 22 are rotated so that thelongitudinal rods are successively presented to the welding head 78along with the circumferential rod. The constant rotation of thestationary wheel 20 ensures that the circumferential wire is maintainedtaut against the longitudinal rods, so that a good weld can be made. Thewelding head 78 may then weld the wire to the next longitudinal rod. Themovement of movable wheel 22 along the rails 26, 28 as the weldingoperation is taking place provides the circumferential wire with aspiral configuration a around the longitudinal rods.

In one embodiment, the welding unit 16 welds wire to the steel rods at1000 Hz with a 400 A current. In this regard, the welding unit 16 offersa number of advantages over the welding machines conventionally used incage manufacturing. Specifically, the welding unit creates less slag andspark while welding, along with creating a stronger weld that is lesstempered than the weld produced by conventional welding units.Additionally, weld time is less with welding unit 16 compared toconventional welding units, which yields reduced cage production timethat can be realized in increased productivity for the manufacturer. Thewelding unit 16 also provides less tempering of the steel rods. Thisallows steel to be used which contains more carbon than can be used withtraditional welding units. Moreover, high carbon steel wire is generallyless expensive than low carbon steel wire thereby providing a decreasein manufacturing costs.

Weld Welding Unit Wire Size Time Ramp Time Welding Current Proposed 8 mmwire 30 ms 10 ms 10 kA 1000 Hz Conventional 8 mm wire 60 ms — 15 kA 50or 60 Hz

As shown in the table above, the weld time of welding unit 16 may behalf the time of a conventional welding unit. This provides extra timefor the welding unit 16 to create a ramp effect using pulse widthmodulation in order to allow the steel to cool relatively slowly over anadditional 10 ms period of time. During this cooling process the carboncontained in the steel is kept misaligned, which permits the steel toretain its malleable properties. This is in contrast to conventionalmanufacturing techniques which utilize multiple heating and coolingcycles for a single weld, which may result in steel that is tempered,where the carbon molecules in the steel align with one another andcreate very hard and brittle portions near the weld area therebyreducing the strength of the overall wire cage.

In one embodiment, the welding operation carried out by the welding head78 uses a pair of rollers and brushes to transfer electrical current tothe wire and longitudinal rods, such as illustrated in FIGS. 3 and 5.However, in another embodiment, which is schematically illustrated inFIG. 6, the welding head 78 has a copper welding contact 110 that formsthe welding arc with the steel rods 112 during welding of wire 114 tothe longitudinal steel rods 112 without the aforementioned rollers andbrushes, which tend to create relatively large resistance that must beovercome. The welding head 78 utilizes two hydraulic cylinders 116, 118to maintain proper position of the copper contact 110. Copper contact110, in one embodiment, is much smaller than that used in conventionalwelding heads, which greatly reduces the weight and cost of the head. Inaddition, the welding unit 78 uses a linear welding head which increasesthe flow of current to the copper contact and steel rods resulting in astronger weld.

The hydraulic cylinders 116, 118 may be controlled to minimize the wearof the copper contact as it contacts the wire and steel rods. The use ofa hydraulic system instead of a pneumatic system allows for lessexpensive “soft copper” to be used as the contact for the welding headrather than “hard copper”. “Soft copper” is less expensive than the“hard” copper alloy which is typically used to make the contacts.

As noted above, a linear welding head may be used rather than rotatingcopper wheels and brushes. This may provide greater efficiency in thewelding circuit as a result in the decrease in the resistance betweenthe connection of the copper contact 110 and the transmission wires 120,which are used to transmit the current from the welding transformer 122to the contact 110. When transmitting 15 kilo-amperes of current, forexample, a change of resistance of even one ohm can make a very largedifference in efficiency. With a linear welding head the connectionbetween the welding transformer 122 and the copper contact 110 is aconstant contact and has a very low resistance compared to copperbrushes contacting the spinning copper wheels.

Rod Radial Spacing Control

Referring again to FIGS. 1 and 2, and with further reference to FIGS. 7Aand 7B, the rod radial spacing control system 14 includes a guide tube124 connected at one end to the hub 60 of the stationary wheel 20 andconnected at an opposite end to a post 126. The guide tube 124 isdesigned to rotate with rotation of the stationary wheel 20. In thisregard, the guide tube 124 is fixed to the hub 60 of the stationarywheel 20 and is coupled to the post 126 through a bearing 128.

A chain mount 130 is mounted to the guide tube 124 and rotates with theguide tube 124. A series of chain guides 136 are mounted to a forwardface of the chain mount 130. The number of chain guides 136 is equal tothe number of rod clamps 64 carried by the spokes 62 of the wheel 20.Chain guides 138, 140, which are in the form of sprockets, are securedto a rear surface of a hub mount 143 that is coupled to the hub 60 ofthe wheel 20. Chain guides 138 are spaced inwardly of chain guides 140.An additional set of chain guides 142, which are also in the form ofsprockets, are mounted to the spokes 62 of the wheel. More particularly,a flange 144 is mounted to each of the spokes 62 and the chain guides142 are coupled to the flanges 144.

Two respective chains 146, 148 are associated with each spoke 62 of thestationary wheel 20. Chain 146 has a first end 150 coupled to a bracket152 to which clamp 64 is connected and a second end 154 connected to acarrier bracket 156. A cylinder 132 is housed within the guide tube 124and includes a ram 134 that is coupled to the carrier bracket 156through a slide block 157. The ram 134 is preferably fixed to the slideblock 157 so as to rotate with the slide block 157. However, thecylinder 132 is arranged within the interior of guide tube 124 so as notto rotate along with guide tube 124. To this end, suitable bearings maybe positioned between the cylinder 132 and the inner wall of guide tube124, so that cylinder 132 does not rotate.

When the ram 134 is retracted, the carrier bracket 156 is moved alongthe guide tube 124 and away from the wheel 20. Similarly, when the ram134 is extended the carrier bracket 156 moves toward the wheel 20.

Chain 148 has a first end 158 that is coupled to the clamp bracket 152and a second end 160 that is coupled to the carrier bracket 156. Whenthe ram 134 is extended, the carrier bracket 156 is pushed toward wheel20 which results in the chains 146, 148 moving in a clockwise direction(in the illustrated figure). As the clamp 64 is coupled to chains 146,148, the clamp 64 will move in response to movement of the carrierbracket 156. Thus, when the ram 134 is extended, the clamps 64 arepushed away from the hub 60 by their respective chains 146, 148. Eachclamp 64 carries a rod guide tube 162 through which the longitudinalrods extend. As such, the rods are pushed away from the hub 60 as theram 134 is extended.

Conversely, when the ram 134 is retracted the ram 134 forces the carrierbracket 156 away from the hub 60. As a result, chains 146, 148 arepulled in a counterclockwise direction. Each clamp 64 is thus movedtoward the hub 60 to decrease the distance of each rod from the hub 60decreasing the diameter of the wire cage. This is particularly evidentby comparing FIGS. 7A and 7B. FIG. 7A shows the clamps 64 at a decreasedradial distance resulting from retraction of the ram 134, and FIG. 7Bshows the clamps at an increased radial distance resulting fromextension of the ram 134.

A linear position sensor is used to detect the linear position of theram 134 and provide a corresponding signal to the control station 18,which may include a computer or similar processor for determining theradial position of the clamps 64 from the position of the ram and movethe welding head described above accordingly. Representatively, thelinear position sensor may be a magnetoresistive transducer-typeposition sensor such as is available from Gefran under its model numberIK1A, although it is understood that any other satisfactory type ofposition sensor may be employed.

Control Station

The control station 18 can be of conventional design and, as such,includes various operator input controls and system monitoring devicesincluding dials, meters, and other displays. The control station 18includes a computer (not shown) or other processor to effectuateoperator control of the cage making process including, but not limitedto automated control of the various components of the cage makingmachine 10 such as those described herein. In one embodiment, thecontrol station 18 includes controls that allow an operator to interfacewith the rod spacing control components to change the diameter of a wirecage, or portions thereof, in real-time. The welding unit 16 can also becontrolled, either manually or in an automated fashion, to respond tochanges in the spacing of the longitudinal rods so that welding head issuitably pivoted toward or away from the longitudinal rods.Additionally, the control station allows an operator to interactivelycontrol the rotational speed of each wheel 20, 22 or execute a storedprogram that independently controls the rotational speed of each wheel20, 22 which may include driving the wheels 20, 22 to rotate atdifferent speeds or in different directions.

Exemplary Wire Cage Contours

As illustrated in FIGS. 8-10, the present invention allows flexibilityin the contour of a wire cage. FIG. 8 shows a schematic for a wire cage164 made with wheel 20 and 22 being rotated at the same velocity. Thewire cage 164 is generally cylindrical in shape and is defined by anumber of longitudinal steel rods 166 joined together by acircumferential wire 168. The circumferential wire 168 has a generallyspiral or helical shape which occurs by moving the movable wheel 22 awayfrom wheel 20 as the wheels 20, 22 are rotated. FIG. 9 shows a wire cage164(a) in which the longitudinal steel rods 166(a) are angled fromend-to-end. The diameter of the wire cage 164(a) is uniform along thelength of the wire cage 164(a). The angling of the rods 166(a) iscreated by rotating the wheels 20, 22 at different speeds. The wire cage164(a) is advantageous in countering the torsional stresses placed onthe wire cage during concrete pipe formation. More particularly, thetwist in the longitudinal rods may be made to oppose the twist generatedby the concrete pipe manufacturing process.

FIG. 10 shows a wire cage 164(b) in which the longitudinal rods 166(b)are angled and the radial spacing of the rods is not uniform along thelength of the cage 164(b). As noted above, the rods can be twisted byrotating the wheels 20, 22 at different speeds and/or directions. Aradial distance of the rods 166(b) from the center axis of the cage164(b) can be achieved by extending and retracting the ram 134 so thatthe position of the rods along their respective spokes varies during thecage making process. It is appreciated that contours and shapes otherthan those shown in FIGS. 8-10 may be achieved through control of wheelrotational speed, wheel translation speed, and translation of the rodclamps.

Various alternatives and embodiments are contemplated as being withinthe scope of the following claims particularly pointing out anddistinctly claiming the subject matter regarded as the invention.

1. An apparatus for manufacturing a wire cage, the apparatus comprising:a first rotating member configured to support a plurality of cage rods;a second rotating member configured to support the plurality of cagerods, the second rotating member spaced from the first rotating memberand the plurality of cage rods extending between the first rotatingmember and the second rotating member; and a drive assembly thatindependently rotates the first rotating member and the second rotatingmember.
 2. The apparatus of claim 1 wherein the drive assembly rotatesthe first rotating member and the second rotating member at differentrotational speeds to effectuate twisting of the plurality of cage rodsextending between the first rotating member and the second rotatingmember.
 3. The apparatus of claim 1 wherein the drive assembly comprisesa first drive motor coupled to the first rotating member to rotate thefirst rotating member and a second drive motor coupled to the secondrotating member to rotate the second rotating member.
 4. The apparatusof claim 1 further comprising a track along which the second rotatingmember may be translated to define the spacing between the firstrotating member and the second rotating member.
 5. The apparatus ofclaim 1 further comprising a wire feed that delivers wire to weld, in aspiral pattern, around the plurality of cage rods.
 6. The apparatus ofclaim 5 further comprising a welding assembly to weld the wire to theplurality of cage rods, the welding assembly including: a welding headsecured to a pivot arm; and means for effecting selective pivotingmovement of the pivot arm to control positioning of the linear weldinghead.
 7. The apparatus of claim 6 wherein apparatus includes a frame,and wherein the pivot arm is pivotably mounted to the frame.
 8. Theapparatus of claim 6 wherein the welding assembly comprises atransformer that allows for maximum current transfer to the wire.
 9. Theapparatus of claim 6 wherein the welding assembly welds the wire to acage rod at approximately 1000 Hz and at approximately 400 A current.10. The apparatus of claim 1 wherein the cage rods are composed of highcarbon steel.
 11. A method of manufacturing a welded wire structure, themethod comprising: securing a plurality of longitudinal steel rods to afirst wheel and a second wheel spaced from the first wheel;independently rotating at least one of the first wheel and the secondwheel; and welding a circumferential wire to the plurality of steel rodsas the first and second wheels are rotated and the second wheel is movedaway from the first wheel.
 12. The method of claim 11 wherein the stepof rotating the first and second wheels includes rotating the firstwheel at a first speed and rotating the second wheel at a second speed,different from the first speed.
 13. The method of claim 11 wherein thestep of rotating the first and second wheels includes rotating the firstwheel in a first direction and rotating the second wheel in a seconddirection, different from the first direction.
 14. The method of claim11 further comprising changing the radial position of the longitudinalsteel rods as the second wheel is moved away from the first wheel.
 15. Awelding system comprising: a linear welding head having a coppercontact; and a pair of hydraulic pistons connected to the linear weldinghead to control positioning of the linear welding head relative to alongitudinal rod and spiral wire used to form a part of a reinforcingcage for a concrete structure.
 16. The welding system of claim 15wherein the copper contact is composed of soft copper.
 17. The weldingsystem of claim 15 further comprising a spool of wire that is controlledto present the spiral wire to the linear welding head.
 18. The weldingsystem of claim 15 further comprising a transformer that is connected tothe copper contact in a manner that allows for maximum current transferto the spiral wire and a longitudinal rod.
 19. The welding system ofclaim 15 configured to weld at 1000 Hz and a 400 A current.
 20. Thewelding system of claim 15 mounted adjacent an assembly that presentslongitudinal rods to be weld to the spiral wire, the assembly including:a first rotating member configured to support a plurality of cage rods;a second rotating member configured to support the plurality of cagerods, the second rotating member spaced from the first rotating memberand the plurality of cage rods extending between the first rotatingmember and the second rotating member; and a drive assembly thatindependently rotates the first rotating member and the second rotatingmember to effectuate orientation changes in the plurality of spinal rodsas defined between the first rotating member and the second rotatingmember.
 21. An apparatus for use with a wire cage making machine andconfigured to change the radial spacing of longitudinal rods that formpart of a wire cage, the apparatus comprising: a guide coupled to awheel that holds the longitudinal rods and is rotated to present therods and connecting wire to a welding unit that welds the connectingwire to the longitudinal rods, wherein the wheel includes a central hub,an outer rim, and spokes extending between the central hub and the outerrim; longitudinal rod clamps mounted to the spokes; a mounting membermovable along the guide; flexible elongated drive members coupling theclamps to the mounting member; and an actuator that moves the mountingmember along the guide, wherein movement of the mounting member changesthe radial position of the clamps relative to the central hub of thewheel.
 22. The apparatus of claim 21 wherein the actuator includes acylinder coupled to the central hub and rotatable with the wheel and aram rotatable with the wheel and connected to the cylinder and the chainmount.
 23. The apparatus of claim 21 further comprising a post thatsupports the guide and a bearing interconnected between the post and theguide that allows the guide to rotate relative to the post in responseto rotation of the wheel.
 24. The apparatus of claim 21 furthercomprising a sensor that detects a position of the mounting member alongthe guide and provides feedback to a controller that determines theradial position of the clamps from the hub.
 25. A wire cage makingmachine comprising: a carriage; a stationary wheel mounted to thecarriage; a movable wheel mounted to and movable along the carriage; awelding unit for welding wire to longitudinal rods carried by thestationary wheel and the movable wheel, the welding unit having awelding head mounted to an arm; and a bracket coupling the arm to thecarriage, wherein the bracket allows the arm to pivot so as to move thewelding head in response to changes in radial position of thelongitudinal rods.
 26. The wire cage making machine of claim 25 whereina linear welding head has a copper contact and a pair of hydraulicpistons connected to the arm to control positioning of the linearwelding head relative to a longitudinal rod and wire.
 27. The wire cagemaking machine of claim 25 wherein the welding unit includes a pair ofrollers and brushes to conduct welding current from a power source to alongitudinal rod and the wire.